Ultraviolet resonance Raman spectroscopy as a probe of protein structure in the fd virus

Resonance Raman spectroscopy can provide details of molecular structure via the enhancement of specific vibrational bands in the spectrum of the scattered light when the laser excitation is tuned to electronic absorption wavelengths of the molecule. The availability of lasers operating in the deep ultraviolet region makes it possible to apply this technique to problems of protein structure. The backbone conformation and the environments of aromatic side chains can be probed via appropriate enhancement of selected vibrational modes. In this article we investigate ultraviolet resonance Raman (UVRR) spectra from the coat protein of the filamentous bacteriophage, fd, in the intact virus and in sodium dodecyl sulfate (SDS) suspension. The results indicate that 1) the protein is completely alpha-helical in the mature virus, but loses a large fraction of its helix content in the SDS micelles. 2) The two tyrosine residues appear to behave as H-bond acceptors in the intact phage but this interaction is lost in the micelles. 3) The tryptophan residue is not solvent-exposed in either protein conformation, although in SDS it is accessible to H/D exchange with the solvent. 4) The three phenylalanine residues are involved in stacking interactions in the intact virus; these are disrupted in the SDS micelles. 5) The single proline residue appears to be in a trans conformation both in the virus and in the micelles.